Monday, December 16, 2013

Soviet signals intelligence and the German Enigma cipher machine

From the mid 1930’s the German Armed forces started using the plugboard Enigma as their main crypto system. The Enigma has received a lot of attention from historians since the solution of this traffic by the codebreakers of Bletchley Park played a role in WWII operations.

Were the Soviets also able to solve the Enigma machine cryptanalytically? Initially there were two main Soviet cryptologic departments during WWII, one under the NKVD’s 5th Special Department and the other under the GRU’s 8th Department. In 1942 the Army’s cryptologic department was absorbed by the NKVD department.
According to historian Matt Aid ‘By the end of World War II, the 5th Directorate controlled the single largest concentration of mathematicians and linguists in the Soviet Union.

With so many talented mathematicians could the Soviets have figured out how to solve the Enigma? Could they have built special cryptanalytic equipment like the British bombes?
Let’s have a look at the available information.

Regarding the theoretical solution of the Enigma:
David Kahn who interviewed KGB General Nicolai Andreev (head of the KGB’s sigint department in the 1970-80's) in 1996 was told that the Soviets knew how to solve the Enigma and although they didn’t have bombes ‘it might have been possible to organize people to replicate the mechanisms work’.

Regarding special cryptanalytic equipment:
The Cryptologia article ‘Summary Report of the State of the Soviet Military Sigint in November 1942 Noticing ‘ENIGMAhas a report from the GRU that says: ‘The research group of our office has revealed the possibility of solving German messages enciphered on the ‘Enigma’ machine, and started to construct equipment, speeding up the solution’

Captured material:
There can be no doubt that during the war both Enigma machines and valid keylists fell into Soviet hands.

1). In December 1941 Enigma machines and documentation were lost by the German 2nd Army.
2). After the surrender of the encircled German forces in Stalingrad in early 1943 Enigma machines and documents plus signals personnel fell into Soviet hands.

3). According to the memoirs of Admiral Golovko documents were retrieved from the sunken U-boat 639 in August 1943: ‘Submarine S-101, which sank U 639 and recovered lists of call-signs and codes which made it possible to keep track of enemy submarines throughout the Northern theatre
4). During the summer ’44 battles several German units were encircled and destroyed. It is safe to assume that a lot of crypto material was lost.

Help from abroad:
During WWII their spy John Cairncross was able to infiltrate Bletchley Park and he gave the Soviets copies of the documents that he had access to. Some dealt with the Enigma.

So it is certain that the Soviets were able to solve Enigma messages thanks to compromised material and the possibility that during the war they managed to retrieve the daily Enigma settings cryptanalytically cannot be discounted. The only way to know for sure is for the Russian government to give researchers access to the wartime files of the NKVD 5th Department.
Another way is to look for information from other available sources. One such source is the report ‘Russian signal intelligence 1941-45’ by Lt Col Fritz Neeb, head of evaluation for NAAS 2 (Signal Intelligence Evaluation Center) of KONA 2 (Signals intelligence Regiment 2) assigned to Army Group Centre in the Eastern Front.

According to Neeb the Soviet signals intelligence organization was as good as or better than the Germans in traffic analysis and direction finding. However it doesn’t seem like they were able to solve German Enigma traffic, at least up to late 1942.
In page 17 of his report he says that during the Stalingrad battle a Soviet 5-figure message was decoded and it contained a signals intelligence report. The report showed that the German units in the area were correctly identified but there was a mistake in their numerical designation. This would imply that the information came from sources other than cryptanalysis since in German messages numbers had to be spelled out.

According to the recent article ‘О ВКЛАДЕ СОВЕТСКИХ КРИПТОГРАФОВ В ПОБЕДУ ПОД МОСКВОЙ’, in late 1942 the Soviet codebreakers analyzed the Enigma cipher machine and developed ways of solving it. However their efforts failed in January 1943 due to new German security measures.

This information seems to be confirmed by the war diary of the German Army’s Inspectorate 7/VI. The March 1943 report of Referat 13 (security of German cipher machines) says that based on the published radio dispatches from Stalingrad Inspectorate 7/VI was asked to give an opinion from the point of view of decipherment.


Auf grund der veröffentlichten Funksprüche asus Stalingrad wurde In 7/VI um ein allgemeines Gutachten gebeten, das die Stellungnahme vom Standpunkt der Entzifferung enthält.

Thus it seems that the Soviet effort to decrypt Enigma messages was identified early and countered by the Germans.

Sources: ‘Russian signals intelligence 1941-45’, Intelligence and National Security article: ‘The Soviets and naval enigma: Some comments’, The History of Information Security: A Comprehensive Handbook chapter 17-‘Eavesdroppers of the Kremlin: KGB sigint during the Cold war’, Cryptologia article: ‘Summary Report of the State of the Soviet Military Sigint in November 1942 Noticing ‘ENIGMA’, Cryptologia article: ‘Soviet comint in the Cold war’, ‘Journal of Contemporary History’ article: ‘Spies, Ciphers and 'Zitadelle': Intelligence and the Battle of Kursk, 1943’, Inspectorate 7/VI Kriegstagebuch, О ВКЛАДЕ СОВЕТСКИХ КРИПТОГРАФОВ В ПОБЕДУ ПОД МОСКВОЙ


  1. To add to your heading 'captured material' there was also incident similar to U-639. After sinking on July 30, 1944 German U-Boat U-250 in very shallow part of the Gulf of Finland off Karelia Isthmus, Soviets raised the sub and recovering some cipher material from it. This was probably similar in that they probably recovered lists of call-signs, and the cipher materials for the months the submarine was to be operating, allowing them to read that particular Kriegsmarine net for submarines in the Baltic for a few months until the usual changes. According to the book ‘The Crown Jewels: The British Secrets at the Heart of the KGB Archives’, in 1942 apart from decrypted messages Cairncross was able to get ‘two volumes of the secret training manual on deciphering, a guide for the reading of the German Enigma key code-named TUNNY and a description of a machine constructed by the British to read the Luftwaffe's cipher traffic.’

    1. Thanks. I’ve written about John Cairncross here: